Lennon and McCartney took equal credit for every song, regardless of who actually wrote what. In some cases, it’s come out who the real songwriter was. In this case, there was disagreement.

John Lenon and Paul McCartney split credit for all the songs they wrote during the Beatles, even if the song was primarily or totally written by just one of them. People like to speculate about who wrote what, and after the Beatles broke up both John's would sometimes say who did, but they didn't always agree.

Who are both Johns?

John Lennon and Paul McCartney :)

Why do you call them both Johns? Is that a Beatles fan inside joke?

"The Two Johns" is usually used for the band They Might Be Giants, who are John Linnell and John Flansburgh (plus a technically rotating backup band, but usually Danny Weiskopf, Dan Miller and Marty Beller).

Hah no, I honestly have no idea why I wrote that accidently. Maybe as someone mentioned I was thinking of TMBGs or something.

Because they are both named ... John?

Paul's name is James, actually.

There isn't much significance on the Beatles side of it. On the computer/algorithm/bayesian/tech/math side it might be moderately significant to some.

On the Beatles side, this is one of the few Lennon/McCartney songs where there was any recorded disagreement as to who contributed what. The results of this don't convince me, and given that one of the two involved is no longer here, it won't ever get settled.

It was on the Beatles' Rubber Soul album, released in 1965.

And the melody is perfect

I have In My Life on the list of songs to be played at my funeral.